The main frame is built from Misumi 40x80 mm aluminum extrusions. The build platform is made from 30x90 mm extrusions. That leaves a void on the underside of the build platform (80 mm high frame vs 30 mm high platform). This void is filled with 50 kg of concrete to give the static part of the machine as much weight as possible.
The machine's four feet also have cast concrete "shoes" which weigh 10 kg each. These shoes sit on a 15mm thick rubber mat (used for dampening vibrations of washing machines), and all of that is placed on a custom made table (26 mm solid beech wood with 80x80 mm spruce wood legs and 40x80 mm cross beams).
Mounting brackets and constructive parts are mostly made from 2.5 mm thick lasercut stainless steel parts, and some aluminum spacer parts.
Mounted on the table is an enclosure with removable acrylic panels to keep noise and dust inside.

Some more core design decisions:
I've opted to work with Misumi aluminum extrusions. These stand out from any other alu extrusions because they are VERY strong. The portal is an "all-around" construction of 30x120 mm alu extrusions which are definitely more rigid than any milled aluminum beam constructions.

The portal is screwed together using 4 M8 screws on every joint, then reinforced with 2.5mm stainless steel brackets which should give me a rock solid portal that is still lighter than a steel construction.
I haven't built it up yet so I can't tell from my own experience. But you can bet that I will put it to the test

/edit:
Almost forgot the most important part:
I will publish all the source files once I get it to work. No sense in publishing it earlier because there surely is some fatal error somewhere right now. If you want to take a closer look, I can send you the step (or SpaceClaim) file by mail. Just send me a PM and please respect confidentiality with the files.

Will keep you guys updated on the build. For now I have ordered screws and nuts worth 650 CHF (omg) and the alu extrusions and X axis rails (1100 EUR). The rest of the linear hardware (2200 EUR) and the CNC parts (don't even want to calculate that) will have to wait because my budget is really blown right now. Will be living on bread and water for the next few months..

Last edited by jonnybischof on August 10th, 2016, 3:15 am, edited 1 time in total.

Will have to read through it and see what's applicable to my design, and where I might run into problems myself.

As for how to mount the thing.. I bought a granite reference plate, 820x570 mm, DIN876/00 (+-4 um surface planarity), some large 90° steel angles and a dial gauge. Yeah, that plate is not quite big enough for the large part, but dude these things are expensive!

I hope I can get the X axis mounted well enough (btw, I failed to do so on my 3D printer prototype - so far). This will be the biggest challenge.
Btw it seems that my X and Y is inverted to the common CNC portal mill "standards". My X is the longest axis whose rails are mounted on the base frame. The portal travels along the X axis and holds the Y axis.

/edit:
Oh, and don't worry, I have taken into account that the alu extrusion length will not be exactly as long as specified. The construction theoretically compensates for any of these errors. The question is just whether I can actually do it in practice...

I also designed a portal mill by myself, made of wood plates - so a cheesemill (Käsefräse ).
Unfortunately it don´t made it to reality up to now. Requested the parts at several suppliers, but came up to 700€ just for the CNC'd wooden parts...

In my design, I dont want the portal to be moved because of the place I intended to place it so I move the milling table. downwash: 1/2 the milling space compared to the footprint

Well, I design my machines with one thing in mind - move as little weight as possible and put as many parts as possible on the static part of the machine.
Therefore, the largest axis must be the static one, and the smaller axes are moved. Moving the whole build platform would mean moving a lot of weight (talking about a machine that is supposed to be very precise, hence needs weight and rigidity wherever possible). So I designed my machine making a very bulky and heavy - but static - x axis, and consecutively lighter Y and Z axes. The result is pretty much what most machines look like - surprise ^^

I don't need speed. I want accuracy and good results. I know that these goals are difficult to achieve with anything but professional CNC workcenters.

One thing I've already learned - I could - should - have used even larger linear rails on the static X axis than my 23mm ones. The price difference is not that big, but the mere weight of the rail increases the machine's rigidity and reduces audible noises. Plus, big linear rails like 30mm width are so strong that the "huge" forces a CNC machine produces appear puny in relationship. That means a longer life, and less probability to run into trouble after a few years of machine service.

/edit: 23mm rails are built for around 3 tons of max. load. That is a little bit more than what occurs on a CNC machine ^^
(moving parts of my machine are around 60 kg in total, but don't forget about acceleration and decceleration forces)

Yep, it's a watercooled spindle. The thing is expensive (watercooling system adds another 500 EUR, but I have some of the expensive parts already laying around from an old PC project) but from what I've gathered so far it is one of the good chinese products. Made in China, but guaranteed quality and customer service by a german company.

The CNC my friend built was made crazy strong and rugged, namely for sign making tasks on wood. However we have put all kinds of aluminum through this machine, making hundreds of R2 parts on it. We've stuck with single flute carbide tips from China, where we can get a dozen for $9 or pay three times that amount for the same product locally (I'm not a fan of the China knock offs...but if the carbide tips are identical, I am all for a deal!)

One thing to consider is chatter. We have struggled to find the best way to secure and clamp down aluminum plate (0.125 inch thick) so that it doesn't vibrate like crazy and cause bits to break. His machine surface is a large piece of MDF and we have drilled and placed brass screw downs all over the place. We've learned a lot over the years! We also have really great luck with vCarve Pro software.

It's priced right and works very well.
We had the 8.0 version and are still learning the new features of the newer one

Over the years we've taught ourselves a few nice tricks. Since metal has a little variance in the thickness, we have tended to make the first cuts very shallow and slow. Then the following ones deeper and a bit faster, since we now have a consistent thickness. Ramps are good too.

For the watercooling, I went for a cheap solution: a small chinese watercooling pump and radiator.

It works very well, but a was afraid it could break and my spindle would overheat, so I made a small Arduino project which monitors the pump speed and the water and spindle temperatures so it can raise and alarm and stop the spindle if it goes beyond limit.

Spindle monitor

Total cost of the solution: about 80€ (Half of this being for the monitor )

I didn't knew what to expect as dissipation from a 2.2 kW spindle, but it turned out this small setup is enough: water temperature raises about 10°C above room temperature, then stabilize even for a long job.

danilius wrote:Looks like we are going to need a new section for CNC machines

Don't wanna kick off a revolution here
I'm just at a development stage where input from you guys will be vital in improving the design or finding errors I can't see.

I've already learned a lot from ems-moederl. The guy really seems to know what he's doing and he put up a huge amount of information on the page and in youtube videos (all in german...).

One major difference between his machines and mine - hopefully not a crucial mistake on my side - is that he aligns the machine base onto the portal. Me, I will have to make a perfectly aligned machine frame and align the portal onto it. That is simpler in theory and build complexity, but it might be a problem if it doesn't work as intended...
The most important challenge here is to design something in a way that it can actually be built in practice like it's supposed to be on the drawing.

I have a lot of experience in watercooling systems for PCs. Here we have basically the same thing, except there's much more energy to be transported, and there is no need to be super silent. PC watercooling systems usually work at a temperature difference between the cooling blocks and the radiator of around 3 K. That is very little and means that the system has a lot of spare capacity to work with. Pair that with the fact that the radiator fans are hardly spinning because you want them to be silent, and there's even more spare capacity.
I have no doubt that a standard PC watercooling system using stronger than usual fans will have no issues at all. If you use a good watercooling pump like an Eheim or a Laing DDC, you don't have to worry about failures. Listen to the pump when it powers up, and before it powers down. Should the pump fail any time soon, you will hear the difference. As long as the sound is ok, the system is very unlikely to fail any time soon.

Software is not much of an issue right now. I can worry about that once the build is real and working. That will take a few months simply because every single step costs $$$$. I will get an EdingCNC controller with Leadshine DM556 drivers. That includes a postprocessor and - afaik - a 2.5D GCode generator. I will probably get a Condacam LT license once the need (for 3D milling) arises.

For Y/Z I see it allows you to have a more compact build, but for the X it does not change anything...

For the drivers I also went for the Leadshines DM556 and I am very happy with them. Alternative would have been closed loop, but I was already above budget
For the controller I eventually bought a board from Mesa. They make industrial quality boards and the quality is superb. It uses an FPCGA for the step-gen, so it can pulse very fast. All their drivers (including FPCGA) are open.
Having said that EdingCNC is making very nice hardware as well, that would probably have been my second choice.

I did the belt drives because I wanted to avoid having to mess with direct drive couplers, and even in Z I actually saved a couple cm in length. Initially I wanted to fold the X motors underneath the machine, but that would come with a longer belt and a bit more difficult construction. I might actually look into this again because it would make the machine look much better if the X motors were tucked away.
Btw. I'm trying to switch from 6mm GT2 belts to 9mm ones. The Misumi calculator said that the 9mm belts would be optimal. I hope robotdigg can make me some nice 9mm pulleys..